Though it is a substrate, homoserine can actually cause partial inhibition of the reaction at higher concentrations, with a Ki of ~2 mM [Shames84]. Substrate inhibition by high levels of ATP has also been observed [Chassagnole01]. ThrB has been subject to kinetic and mechanistic analysis [Shames84, Huo96]. The enzyme appears to have a second, regulatory binding site for L-homoserine [Shames84, Chassagnole01]. Site-directed mutagenesis has confirmed the role of Arg234 and the His residues H139 and H205 in substrate binding [Huo96a].

ThrB is required for growth of pdxB mutants on glucose and 3-hydroxyhomoserine or D-glycolaldehyde [Zhao96a]. Later, thrB was identified as a multicopy suppressor of the PLP auxotrophy of a pdxB deletion strain. ThrB was found to be part of a serendipitous metabolic pathway that produces an intermediate of the pyridoxal 5'-phosphate biosynthesis I pathway, 4-phospho-hydroxy-L-threonine, that lies downstream of PdxB [Kim10c]. The 4-hydroxy-L-threonine kinase activity of ThrB that is required for this pathway had already been identified in vitro [Shames84a]. The pathway diverts 3-phosphohydroxypyruvate from serine biosynthesis [Kim10c].